Fractureproofed frangible body and production thereof



Feb. 13, 1951 M. H. FRISBIE ET AL FRACTUREPROOFED FRANGIBLE BODY AND PRODUCTION THEREOF 7 Filed Aug. 21, 1945 IN V EN TORS,

ATTO/M/EX Patented Feb. 13, 1951 FRACTUREPROOFED FRANGIBLE BODY AND PRODUCTION THEREOF Marshall H. Frisbie, Hamden, and Shirley P. Morse, East Haven, Conn., assignors to The A. 0. Gilbert Company, New Haven, Conn., a

corporation of Maryland Application August 21, 1945, Serial No. 611,882

4 Claims.

This invention relates to construction inhibiting fracture of frangible small rotor bodies, as for instance the molded insulative core body of a commutator for a small electric motor or the like, that tends to result from forcing the body onto a motor shaft with a press fit. The invention yields analagous advantages when practiced or incorporated in the construction of any body of frangible substance containing a hole or holes into which oversize plugs are to be forced with a press fit. Our copending application, Serial No. 176,326, filed July 28, 1950, claims certain methods herein disclosed for producing the improved constructions herein claimed.

Attempts to press even a slightly oversize knurled metal shaft endwise with a tight fit into or through a relatively undersize hole in a small rotor body of molded condensation product, such as phenolic thermosetting compositions, urea resins, etc., occasion considerable trouble from chipping or cracking of the hard and brittle insulative body of the rotor. Exacting and costly tolerance of fits has heretofore been resorted to for avoiding the occurrence of these defects.

A main object of these improvements is to avoidfracturing of a frangiblerotor body when being mounted on its shaft by press fit telescopic assemblage and without requiring extremely precise accuracy of fit of the shaft in its hole.

A contributory object is to provide a hollow frangible body bushed by a lining of such nature that the lining forms a hole that will be dimensionally stable but will accommodate itself to the axially sliding fit of a somewhat oversize shaft or plug pin pressed lengthwise thereinto without transmitting to the frangible body itself any stresses capable of chipping or breaking it, the lining remaining bonded to and positively constrained by the surrounding non-yielding frangible body.

It is a further object of the invention to pro duce a fracture inhibiting composite rotor body incorporating a lining bushing for a shaft hole therein by bonding the bushing to the insulative body of the rotor in the same application of heat that accomplishes the molding and permanent thermosetting of the plastic material of the rotor body.

It is a further object to make use of a fracture inhibiting bushing having a wall composed of plural or laminated layers.

The foregoing and other aims will appear in greater particular from the following description of an illustrative embodiment of the invention having reference to the appended drawings wherein:

Fig. l is a perspective view of a rotor in the form of a small motor commutator having a frangible insulative hub or core body partly broken away to expose features of the present improvement.

Fig. 2 is a corresponding perspective View of an armature shaft having a portion knurled to enlarge its outside diameter for press fit assemblage with the core body of Fig. 1.

Fig. 3 represents a strip of impregnated paper partially rolled upon itself to form the laminated wall of a fracture inhibiting bushing that is incorporated in the composite commutator core of Fig. 1.

Fig. 4 shows a bushing formed of the impreg nated roll of paper in Fig. 3 sleeved closely around a mandrel stationed centrally of a mold cavity suited to produce the commutator of Fig. 1.

Fig. 5 shows the knurled shaft and commutator in assembled relation and partially broken away.

We have found the following to be one successful way of producing a, composite, plug receptive, insulative body incorporating the fracture inhibiting features of this invention. We may first provide a suitable mold, as for instance that described in U. S. Patent 1,578,793 granted March 30, 1926, to V. G. Apple, which, as represented in Fig. 4 hereof, may include a hollow die i2 provided with a vertically movable plunger l3 having a hole l5 slidably receiving a vertical mandrel I 4 approximately of the same diameter as the unknurled portion of a motor shaft ll. Upon this shaft the finished commutator of Fig. 1 is to be mounted fixedly as shown in Fig. 5 by inserting the shaft endwise and telescopically into or through the hole in the commutator core that is produced by mandrel l4.

Mandrel M has fixed thereon a discal flange is which during the molding process fills the bottom end of the mold cavity in die 112 but rises with the mandrel in such cavity to eject the finished commutator whenever the mandrel slides upward through its guide hole l6 in die I2 after completion of the molding operation.

There is first wound upon or sleeved telescopi- '5 IL face of bushing 22 and the retaining wall of the mold there then placed a preferably powd red condensation product of the: ting cc tion such as a phenolic or urea iESlil in s quantity to fill the ty space in cavity the case of a small coir dutator as pr trated the w. l of t e mold ton cylindrical commutator snell 24 o conductive metal which forms, at least in part, the retaining wall of the mold cavity because such shell is in serted in the mold cavity is in a r anr r to corn fine and become bonded to the insulative core body 25 of the commutator.

After the molding cavity has been filled with the powdered condensation product, plunger is forced downward into its position shown in Fig. 4 and while in this position the mold its entire contents are heated until the condensation product first melts to a liquid which fills and conforms to all faces of the mold cavity eluding bushing F22 and metallic shell is well understood in plastic molding art molten composition then permanently harden-s or sets in its mold determined form and becomes the hard and frangible insulative core body of the commutator.

During this thermosetting process the 1? coils 23 of bushing become bonded to e:

setting substance with which they cg hated and likewise the bushing as a whole be" comes fixedly bonded to the insulative body of the commutator as embedded lining or facing for the shaft hole possessing a degree of resilience.

The mold plunger It can now be lifted and mandrel [4 together with the complete con1mu-- tator can be withdrawn from the die, mandrel 14 preferably being free to slide relatively both to the hollow die l2 and to the plunger [3.

The bushing 22 has now become in effect a unitary part of the insulative body of the commutator but retains some of the characteristics of a roll of paper. Due to these retained characteristics the bushing is found to possess sufficient compressibility and resilience to admit in telescopic manner to the commutator hole the somewhat oversize knurled portion 26 of a shaft ll that can be comparatively larger in relation to the hole size than would be possible in the absence of such bushing. When a knurled shaft is forced endwise into a thus bushed frangible core body wl h a tight press fit it is found that the yielding ability of bushing inhibits chipping, cracking and fracture of the hard frangible surrounding core body by which it is nevertheless positively constrained. The bushing is found to cling fixedly and dependably to the shaft so that there results a securely flXEd mounting of the commutator upon its shaft by the ordinary method of telescopic press-fit assemblage.

As one example of practical sizes and relationships illustrated in the drawings, the insulative core body may be 1 in outside diameter and the shaft hole may be approximately 9 in diameter lined by a coiled paper bushing of about a e total thickness of laminated wall. These diameters approx nate the assem blage will be effective witl -t whose unknurled portion. .1865" dian ter and whose knurled portion be a of .189" diameter or a ma: mum of .191" meter. suitable thermose rng liquio with which to impregnate paper 23 is phenol aldehyde or red .1. The paper is fed in strip form through a resin.

dip and then through a drying oven which partially dries the resin. The strip thus impregnated is then wound onto a mandrel and in this condition. rolled between heated rolls. A partial cure of the impregnating material takes place and a hi h polish of the mandrel surface permits the resulting paper bushing to be slipped off from the end of the mandrel without sticking. This paper may be .008 thick and bushing 22 may consist of a, coil of four convolutions of the paper. Paper having a content of cotton rag has been found to be suitable.

Obviously the application of this invention to any kind of pin or plug receiving hole in a solid body of frangible molded material will serve to protect the body from chippin and cracking when oversize pins or plugs are forced thereinto with a press fit. The same advantages will result, namely in preventing the transmission of stresses to the frangible body which otherwise could fracture it. Therefore the appended claims are intended to cover not only the particular sti tures herein described and illustrated as s...ccessful embodiments of the invention but are directed to all equivalents and substitutes for such structures as fall fairly within the broadest interpretation of the claim language.

We claim:

1. A composite frac'areproof rotor body for press on a shaft, including a relaid frangible homogeneous hub body i thermosetting plastic material conaft hole lined by a tubular bushing edly lodged in said hole comprising a wind- I of compressible sheet material coiled into a hollow cylindrical roll of mutually overlapping convolutious receptive to said shaft.

2. A composite fractureproof rotor body for press fit assemblage on a shaft, including a relatively rigid frangible homogeneous hub body of hardened thermosetting plastic material contain- 11 3 shaft hole lined by a tubular bushing fir. lodged said hole comprising a winding of compressible sheet material coiled into a hollow cylindrical roll of mutually overlapping convolutions receptive to said shaft impregnated with a cured thermosettlng composition bond ing said convolutions to one another and bonding the outer one of said convolutions to said thermosetting plastic material of the said hub body.

3. A rotor for dynamo-electric machines including in combination, a metallic shaft having a peripheral surface slightly ridged in a straight axial direction, a commutator core containing a shaft hole comprising a relatively rigid frangible homogeneous body of hardened thermosetting plastic material, and a tubular bushing fixedly lining said hole comprising a continuous winding of compressible sheet material coiled into a hollow roll of mutually overlapping convolutions having. a press fit on said ridged surface of said shaft.

4. A composite fractureproof rotor body for fit assemblage on a shaft, including a relatively rigid frangible homogeneous hub body of hardened thermosetting plastic material contai a shaft hole fixedly lined by a tubular bus ing comprising a continuous winding of compressible sheet material coiled into a hollow cylindrical *oll of mutually overlapping convolutiors rece 'e to said shaft, said coiled sheet mate ial being impregnated with a cured thermcsetting com-c sition bonding said convolutions to one another and bonding the outer one s of said convolution; to said thermosetting pias- Nu g ber tic material of said commutator core. 263,075

MARSHALL H. FRISBIE. 472,529

SHIRLEY P. MORSE. 1 5 ,902

REFERENCES crmn 124913708 The following references are of record in the 43 3 file 01 this patent: -2323 3 UNITED STATES PATENTS 10 2:3'1 1' 5 Number Name Date 1 96,198 B11811 Oct. 26, 1869 Name Date Brown Nova-28, 1882 Doren Apr. 12, 1892 Egner Jan. '7, 1908 Pettersen Apr. 22, 1913 Kempton Dec. 27, 1921 Himes Met. 18, 1924 Apple Jan. 30, 1934 Cotterman Jan. 4, 1938 Moeiier Apr. 13, 1943 Korte May 18, 1943 

